Two-dimensional photonic crystal surface-emitting laser

ABSTRACT

A two-dimensional photonic crystal formed by arranging in a lattice pattern a medium having a refractive index different from that of a medium layer formed near an active layer. The two-dimensional photonic crystal includes a distributed-feedback control photonic crystal in which a light propagating through the active layer as a core is subjected to a two-dimensional distributed feedback within a plane of the active layer, and the light is not radiated in a direction normal to the plane of the active layer, and a surface-emission control photonic crystal in which the light is radiated in the direction normal to the plane of the active layer, which are superimposed with each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/JP2007/050818 filed on Jan.19, 2007, the entire content of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a two-dimensional photonic crystalsurface-emitting laser.

2. Description of the Related Art

Photonic crystals are periodic optical structures formed by arranging amedium having a refractive index different from a refractive index of,for example, semiconductor, with a period on the order of wavelength oflight, and applications thereof to various optical devices are beingstudied.

Examples of the optical devices using the photonic crystals include atwo-dimensional photonic crystal surface-emitting laser. Conventionaltwo-dimensional photonic crystal surface-emitting lasers are disclosedin, for example, Japanese Patent Application Laid-open No. 2000-332351,Japanese Patent Application Laid-open No. 2003-23193, and JapanesePatent Application Laid-open No. 2004-296538. For example, FIG. 11 is anexploded perspective view of a two-dimensional photonic crystalsurface-emitting laser 100′ disclosed in Japanese Patent ApplicationLaid-open No. 2000-332351. The two-dimensional photonic crystalsurface-emitting laser 100′ includes a confinement layer 102′, a lowercladding layer 103′, an active layer 104′, and an upper cladding layer105′ grown in that order on a substrate 101′. The confinement layer 102′is formed of n-InP semiconductor and contains air holes 108′ formed in asquare-lattice pattern arrayed at a predetermined two-dimensionalperiod. Thus, the air holes 108′ form a photonic crystal in which airmedium having a refractive index different from that of the n-InPsemiconductor is arrayed periodically. The active layer 104′ has amultiple-quantum well (MQW) structure using GaInAsP semiconductormaterial and emits a light when a carrier is injected into the activelayer 104′. The lower cladding layer 103′ is formed of n-InPsemiconductor and the like. The upper cladding layer 105′ is formed ofp-InP semiconductor. The lower cladding layer 103′ and the uppercladding layer 105′ sandwich the active layer 104′, and thereby a doubleheterojunction is formed to confine the carrier. Thus, the carrier thatcontributes to light emission is confined in the active layer 104′. Inthis state, an electrode 106′ made of Au is formed on a top surface ofthe upper cladding layer 105′ and an electrode 107′ made of Au is formedon a bottom surface of the substrate 101′.

When a voltage is applied between the electrodes 106′ and 107′, theactive layer 104′ emits a light, so that a light spreading as anevanescent wave from the active layer 104′ is distributed in thetwo-dimensional photonic crystal formed in the confinement layer 102′.The two-dimensional photonic crystal has a two-dimensional distributedfeedback effect. Therefore, similar to a distributed-feedback laserusing a typical one-dimensional grating, laser oscillation occurs withthe two-dimensional photonic crystal. Furthermore, thedistributed-feedback effect of the two-dimensional photonic crystaloccurs two dimensionally, so that a coherent single-mode oscillationoccurs over a large area of the two-dimensional plane. As a result,surface emission occurs with a single-mode laser light. Principles ofthe two-dimensional distributed feedback and the surface emission of thetwo-dimensional photonic crystal surface-emitting laser 100′ aredescribed below in relation to a wave number space of thetwo-dimensional photonic crystal.

A light that can distributed feedback-operate in the two-dimensionalsquare-lattice photonic crystal operates at X-point, M-point, andΓ-point among symmetric points in a reciprocal lattice space (wavenumber space) of the photonic crystal. The Γ-point is a point at which awave number vector k is represented by k=pb₁+qb₂, where p and q arearbitrary integers and b₁ and b₂ are reciprocal primitive vectors withminimum magnitudes in a square-lattice. The reciprocal primitive vectorsb₁ and b₂ are perpendicular to each other and their magnitudes are 2π/awhere “a” is a lattice constant of the photonic crystal. Similarly, theX-point is a point at which a wave number vector k is represented byeither k=(p+(½))b₁+qb₂ or k=pb₁+(q+(½))b₂. The M-point is a point atwhich a wave number vector k is represented by k=(p+(½))b₁+(q+(½))b₂.

On the other hand, a light that can distributed feedback-operate in thetwo-dimensional triangular-lattice photonic crystal operates at M-point,K-point, and Γ-point among symmetric points in a wave number space ofthe photonic crystal. The Γ-point is a point at which a wave numbervector k is represented by k=pb₁+qb₂, where p and q are arbitraryintegers and b₁ and b₂ are reciprocal primitive vectors with minimummagnitudes in a triangular-lattice. In this case, the reciprocalprimitive vector b₁ and b₂ make an angle of 60 degrees therebetween, andtheir magnitudes are 4π/(√3a) where “a” is a lattice constant of thephotonic crystal. Similarly, the M-point is a point at which a wavenumber vector k is represented by one of k=(p+(½))b₁+qb₁,k=pb₁+(q+(½))b₂ and k=(p−(½))b₁+(q+(½))b₂. The K-point is a point atwhich a wave number vector k is represented by eitherk=(p+(⅓))b₁+(q+(⅓))b₂ or k=(p−(⅓))b₁+(q+(⅔))b₂.

The two-dimensional photonic crystal surface-emitting lasers disclosedin Japanese Patent Application Laid-open No. 2000-332351 employs theΓ-point of either the two-dimensional square-lattice photonic crystal orthe two-dimensional triangular-lattice photonic crystal as an operatingpoint of two-dimensional distributed feedback.

A principle of the two-dimensional distributed feedback is described inrelation to diffraction of a light by a photonic crystal lattice. Thediffraction of a light in a periodic structure such as a crystal latticemeans that a light with a wave number vector k changes to a light with awave number vector of k′=k+p′b₁+q′b₂, where p′ and q′ are arbitraryintegers and b₁ and b₂ are reciprocal primitive vectors. Assuming that alight with a wave number vector k=pb₁+qb₂, that is, a light at theΓ-point, is diffracted such that p′=−2p and q′=−2q are satisfied, alight after diffraction has a wave number vector k′=−k. That is, thelight at the Γ-point is coupled with a wave that travels in a directionopposite to a direction of a light before diffraction. Because lightsthat travel in opposite directions are coupled with each other,distributed feedback occurs. When a light is diffracted such thatp′=−p+q and q′=−q−p are satisfied, a wave number vector of a diffractedlight is represented by k′=qb₁−pb₂. In this state, the light is coupledwith a wave tilted by 90 degrees from a light before diffraction in thecase of a square-lattice, and with a wave tilted by 120 degrees from alight before diffraction in the case of a triangular-lattice.Furthermore, when a light is diffracted such that p′=−p−q and q′=−q+pare satisfied, a wave number vector of a diffracted light is representedby k′=−qb₁+pb₂. In this state, the light is coupled with a wave tiltedby −90 degrees from a light before diffraction in the case of asquare-lattice, and with a wave tilted by −120 degrees from a lightbefore diffraction in the case of a triangular-lattice. Thus, the lightat the Γ-point is fed back to an original position, being diffracted atan arbitrary position on a crystal lattice and coupled with a wave thattravels in the abovementioned predetermined direction. That is, thetwo-dimensional distributed feedback occurs with the light at theΓ-point.

A principle of the surface emission is also described in relation todiffraction of a light. When a light at the Γ-point is diffracted suchthat p′=−p and q′=−q are satisfied, k′=0 is obtained. The fact that awave number vector k′ in a two-dimensional in-plane is zero (k′=0) meansthat the light travels in a direction normal to a plane of a photoniccrystal. That is, the light at the Γ-point has such property thatsurface emission occurs due to an effect of grating couple, with whichthe light is diffracted and travels in a direction normal to the planeof the photonic crystal. As a result, the light at the Γ-pointdistributed-feedbacks two-dimensionally, and surface-emits as well.

As described above, the two-dimensional photonic crystalsurface-emitting laser causes surface emission with a light at theΓ-point in a wave number space of the photonic crystal formed on theconfinement layer. The surface emission is achieved as a coherentsingle-mode laser light over a large area of a two-dimensional plane.

However, in the conventional two-dimensional photonic crystalsurface-emitting lasers, if a two-dimensional distributed feedbackeffect of the photonic crystal structure is optimized to improve thein-plane optical confinement, the intensity of the surface emissiondecreases. On the other hand, if the surface emitting property of thephotonic crystal structure is optimized to increase the intensity of thesurface emission, the in-plane optical confinement degrades. Thus, thetwo-dimensional distributed feedback effect and the surface emittingproperty cannot independently be optimized.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an aspect of the present invention, there is provided atwo-dimensional photonic crystal surface-emitting laser including anactive layer that emits a light with a carrier injection; a medium layerformed near the active layer; and a two-dimensional photonic crystalformed by arranging a medium having a refractive index different fromthat of the medium layer in a lattice pattern. The two-dimensionalphotonic crystal includes a distributed-feedback control photoniccrystal in which a light propagating through the active layer as a coreis subjected to a two-dimensional distributed feedback within a plane ofthe active layer, and the light is not radiated in a direction normal tothe plane of the active layer, and a surface-emission control photoniccrystal in which the light is radiated in the direction normal to theplane of the active layer. The distributed-feedback control photoniccrystal and the surface-emission control photonic crystal aresuperimposed with each other.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a two-dimensional photonic crystalsurface-emitting laser according to a first embodiment of the presentinvention;

FIG. 2 is an exploded perspective view of the two-dimensional photoniccrystal surface-emitting laser shown in FIG. 1;

FIG. 3 is a perspective backside view of the two-dimensional photoniccrystal surface-emitting laser shown in FIG. 1;

FIG. 4 is a plan view of a portion of a two-dimensional photonic crystalwith air holes arrayed on a GaAs photonic crystal layer shown in FIG. 2;

FIG. 5 is a plan view of a portion of a two-dimensional photonic crystalwith air holes arrayed on a GaAs photonic crystal layer in a secondembodiment of the present invention;

FIG. 6 is a plan view of a portion of a two-dimensional photonic crystalwith air holes arrayed on a GaAs photonic crystal layer of thetwo-dimensional photonic crystal surface-emitting laser according to athird embodiment of the present invention;

FIG. 7 is a plan view of a portion of a two-dimensional photonic crystalwith air holes arrayed on a GaAs photonic crystal layer of thetwo-dimensional photonic crystal surface-emitting laser according to afourth embodiment of the present invention;

FIG. 8 is a plan view of a portion of a two-dimensional photonic crystalwith air holes arrayed on a GaAs photonic crystal layer of thetwo-dimensional photonic crystal surface-emitting laser according to afifth embodiment of the present invention;

FIG. 9 is an exploded perspective view of a two-dimensional photoniccrystal surface-emitting laser according to a sixth embodiment of thepresent invention;

FIG. 10 is an exploded perspective view of a two-dimensional photoniccrystal surface-emitting laser according to a seventh embodiment of thepresent invention; and

FIG. 11 is an exploded perspective view of a conventionaltwo-dimensional photonic crystal surface-emitting laser.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are explained below indetail with reference to the accompanying drawings. The presentinvention is not limited to the following embodiments.

A two-dimensional photonic crystal surface-emitting laser 100 accordingto a first embodiment of the present invention includes two types ofsquare-lattice photonic crystals having different lattice constants andsuperimposed one on the other. The two-dimensional photonic crystalsurface-emitting laser 100 emits from its surface a light with thevacuum wavelength of 980 nanometers.

FIG. 1 is a perspective view of the two-dimensional photonic crystalsurface-emitting laser 100; FIG. 2 is an exploded perspective view ofthe two-dimensional photonic crystal surface-emitting laser 100; andFIG. 3 is a perspective backside view of the two-dimensional photoniccrystal surface-emitting laser 100. The two-dimensional photonic crystalsurface-emitting laser 100 includes the following layers grown on ann-GaAs substrate 101. That is, an AlGaAs lower cladding layer 102 with athickness of 4000 nanometers, a GaAs lower separate confinement layer103 with a thickness of 100 nanometers, an InGaAs/GaAsP MQW active layer104 with a thickness of 35 nanometers and a gain peak wavelength of 980nanometers in terms of the vacuum wavelength, a GaAs upper separateconfinement layer 105 with a thickness of 70 nanometers, a GaAs photoniccrystal layer 106 with a thickness of 130 nanometers and containingphotonic crystals, a GaAs spacer layer 107 with a thickness of 50nanometers, an AlGaAs upper cladding layer 108 with a thickness of 2000nanometers, and a GaAs contact layer 109 with a thickness of 4000nanometers are grown on the n-GaAs substrate 101.

An upper electrode 110 of gold in a circular shape with a diameter of 50micrometers is formed on an upper surface of the GaAs contact layer 109,and an insulating film 112 is arranged around the upper electrode 110. Alower electrode 111 of gold is formed on a bottom surface of the n-GaAssubstrate 101. The lower electrode 111 includes an aperture 113 in acircular shape with a diameter of 100 micrometers. An antireflectioncoating film 114 of a dielectric material is formed on the aperture 113.

The two-dimensional photonic crystal surface-emitting laser 100 ismanufactured by the following method. The AlGaAs lower cladding layer102, the GaAs lower separate confinement layer 103, the InGaAs/GaAsP MQWactive layer 104, and the GaAs upper separate confinement layer 105 aregrown on the n-GaAs substrate 101 by metal organic chemical vapordeposition (MOCVD) or molecular beam epitaxy (MBE). Meanwhile, an AlGaAsetch-stop layer (not shown), the GaAs contact layer 109, the AlGaAsupper cladding layer 108, the GaAs spacer layer 107, and the GaAsphotonic crystal layer 106 are grown on a p-GaAs substrate (not shown)by MOCVD or MBE.

A resist pattern is formed on the p-GaAs substrate (not shown) byelectron beam lithography. The resist pattern is transferred onto theGaAs photonic crystal layer 106 to form air holes 115 and 116. Thereby,a two-dimensional photonic crystal in which a distributed-feedbackcontrol photonic crystal and a surface-emission control photonic crystalare superimposed one on the other is formed. The GaAs photonic crystallayer 106 on the surface of the p-GaAs substrate (not shown) and theGaAs upper separate confinement layer 105 on the surface of the n-GaAssubstrate 101 are bonded together by wafer fusion. The p-GaAs substrate(not shown) is then removed by mechanical polishing and selective wetetching. The AlGaAs etch-stop layer (not shown) is also removed byselective wet etching. The upper electrode 110 is formed on the uppersurface of the GaAs contact layer 109 and the lower electrode 111 isformed on the bottom surface of the n-GaAs substrate 101 by electronbeam evaporation or a resistance heating evaporation. The insulatingfilm 112 and the antireflection coating film 114 are formed by electronbeam evaporation. The above obtained wafer is cut out in a predeterminedsize, resulting in the two-dimensional photonic crystal surface-emittinglaser 100.

The GaAs photonic crystal layer 106 in the two-dimensional photoniccrystal surface-emitting laser 100 manufactured in the above mannerincludes the circular air holes arrayed in a lattice pattern as mediahaving a refractive index different from that of GaAs. Thus, atwo-dimensional photonic crystal is formed in the GaAs photonic crystallayer 106.

FIG. 4 is a plan view of a portion of the two-dimensional photoniccrystal with the air holes 115 and 116 arrayed on the GaAs photoniccrystal layer 106. The air holes 115 form a distributed-feedback controlphotonic crystal with a lattice L1 as a primitive cell. The air holes116 form a surface-emission control photonic crystal with a lattice L2as a primitive cell. A lattice constant a1 of the lattice L1 is 205nanometers. A radius of the air hole 115 is 49.2 nanometers, which is0.24 times the lattice constant a1. A mode refractive index of a lightthat propagates in the InGaAs/GaAsP MQW active layer 104 is 3.37.Therefore, if a mode wavelength is defined as an effective wavelength ofa light that propagates in the InGaAs/GaAsP MQW active layer 104 as acore, the mode wavelength of the light with the vacuum wavelength of 980nanometers is 290 nanometers. That is, the lattice constant a1 of thelattice L1 corresponds to 1/√2 times the mode wavelength of the lightwith the vacuum wavelength of 980 nanometers.

The lattice L2 is arrayed such that a crystal orientation of the latticeL2 is tilted by 45 degrees from a crystal orientation of the lattice L1.A lattice constant a2 of the lattice L2 is 290 nanometers that is equalto the mode wavelength of the light with the vacuum wavelength of 980nanometers. A radius of the air holes 116 is 30.8 nanometers, which is0.15 times the lattice constant a1. The air hole 116 is arrayed in themiddle of a predetermined two of the air holes 115.

Principles of a two-dimensional distributed feedback and a surfaceemission of the photonic crystal according to the first embodiment aredescribed below. As described above, the lattice constant a1 is 1/√2times the mode wavelength of the light with the vacuum wavelength of 980nanometers. That is, the mode wavelength of the light is √2a1 andtherefore, the magnitude of its wave number is 2π/(√2a1). Meanwhile,reciprocal primitive vectors b₁ and b₂ of the lattice L1 are b₁=(2π/a1,0) and b₂=(0, 2π/a1). In this state, magnitude of wave number vector kat the M-point is represented by k=(p+(½))b₁+(q+(½))b₂. Therefore, whenp=q=0 is assumed, k=(½)b₁+(½)b₂=(π/a1, π/a1) is obtained, and therebythe magnitude of the wave number vector k becomes 2π/(√2a1). Thus, themagnitude of the wave number of the mode wavelength of the light isequal to the magnitude of the wave number vector at the M-point. As aresult, the light with the vacuum wavelength of 980 nanometers operatesat the M-point in relation to the distributed-feedback control photoniccrystal.

When a light with the wave number vector corresponding to the wavenumber vector of k=(½)b₁+(½)b₂ at the M-point is diffracted due to acrystal lattice of the distributed-feedback control photonic crystal,the wave number vector changes to k′=(p′+(½))b₁+(q′+(½))b₂, where p′ andq′ are arbitrary integers. In this state, when the light is diffractedsuch that p′=−1 and q′=−1 are satisfied, k′ equals to −k. Thus, thelight with a wave number vector corresponding to the wave number vectorat the M-point is coupled with a wave that travels in a directionopposite to a travelling direction of the light before diffraction.Furthermore, when p′=0 and q′=−1 are assumed, k′=(½)b₁−(½)b₂ isobtained, which means that the light with a wave number vectorcorresponding to the wave number vector at the M-point is coupled with awave that travels in a direction tilted by 90 degrees from thetravelling direction of the light before diffraction. Moreover, whenp′=−1 and q′=0 are assumed, k′=−(½)b₁+(½)b₂ is obtained, which meansthat the light with a wave number vector corresponding to the wavenumber vector at the M-point is coupled with a wave that travels in adirection tilted by −90 degrees from the travelling direction of thelight before diffraction. Thus, the light with the vacuum wavelength of980 nanometers and thus a wave number vector corresponding to that atthe M-point in a wave number space is subjected to two-dimensionaldistributed feedback by the distributed-feedback control photoniccrystal, and thereby laser oscillation is achieved.

However, the wave number vector k′ of the light after diffraction is notzero (k′=0) even when any integers are substituted for p′ and q′.Therefore, surface emission does not occur by the distributed-feedbackcontrol photonic crystal.

A principle of a surface emission is described below. The crystalorientation of the lattice L2 of the surface-emission control photoniccrystal is tilted by 45 degrees from the crystal orientation of thelattice L1 of the distributed-feedback control photonic crystal and thelattice constant of the lattice L2 is √2 times the lattice constant ofthe lattice L1. Thus, when reciprocal primitive vectors of thesurface-emission control photonic crystal selected such that theirmagnitudes are minimum are represented by b₁′ and b₂′, they have thefollowing relationship with the reciprocal primitive vectors b₁ and b₂of the distributed-feedback photonic crystal. Specifically,b₁′=(½)b₁+(½)b₂ and b₂′=−(½)b₁+(½)b₂. In this state, a typical wavenumber vector k of a light obtained by laser oscillation due todistributed feedback by the distributed-feedback control photoniccrystal, k=(½)b₁+(½)b₂, can be represented by k=b₁′. This corresponds tothe case where p=1 and q=0 are assumed for a wave number vector k at theΓ-point in a reciprocal lattice space of the surface-emission controlphotonic crystal, where k=pb₁′+qb₂′. That is, the light obtained bylaser oscillation due to distributed feedback by thedistributed-feedback control photonic crystal operates at the Γ-point inrelation to the surface-emission control photonic crystal.

As described above, the light having a wave number vector correspondingto that at the Γ-point is diffracted by the phonic crystal lattice totravel in a direction normal to a plane of the photonic crystal, andthereby surface emission occurs. That is, the light obtained by laseroscillation due to distributed feedback by the distributed-feedbackcontrol photonic crystal realizes surface emission by thesurface-emission control photonic crystal.

Thus, the two-dimensional photonic crystal surface-emitting laseraccording to the first embodiment is formed such that thetwo-dimensional distributed feedback and the surface emission arerealized using different photonic crystal lattices. Therefore, astructure of each of the photonic crystal lattices can be independentlydesigned so that a two-dimensional distributed feedback effect and asurface emitting property are independently optimized. For example, astructure of the distributed-feedback control photonic crystal isdesigned to enhance a distributed feedback effect, and a structure ofthe surface-emission control photonic crystal is designed to increaseintensity of surface emission by adjusting sizes of air holes.

A two-dimensional photonic crystal surface-emitting laser according to asecond embodiment of the present invention is described below. Thetwo-dimensional photonic crystal surface-emitting laser according to thesecond embodiment has a similar structure to that shown in FIG. 1 andcan be manufactured by the same manufacturing method as that describedin the first embodiment. However, a lattice constant and a crystalorientation of a surface-emission control photonic crystal formed on aGaAs photonic crystal layer are different from those described in thefirst embodiment.

FIG. 5 is a plan view of a portion of a two-dimensional photonic crystalwith air holes 215 and 216 arrayed on a GaAs photonic crystal layer ofthe two-dimensional photonic crystal surface-emitting laser according tothe second embodiment. The air holes 215 form a distributed-feedbackcontrol photonic crystal with a lattice L3 as a primitive cell, and theair holes 216 form a surface-emission control photonic crystal with alattice L4 as a primitive cell. Similar to the first embodiment, alattice constant a1 of the lattice L3 is 205 nanometers and a radius ofthe air hole 215 is 49.2 nanometers, which is 0.24 times the latticeconstant a1.

The lattice L4 is arrayed with the same crystal orientation as that ofthe lattice L3, and a lattice constant a2 of the lattice L4 is 410nanometers. A radius of the air holes 216 is 30.8 nanometers, which is0.15 times the lattice constant a1. The air hole 216 is arrayed in themiddle of a predetermined two of the air holes 215.

Principles of two-dimensional distributed feedback and surface emissionof the photonic crystal according to the second embodiment are describedbelow. The distributed-feedback control photonic crystal with thelattice L3 as a primitive cell is a square-lattice and has a latticeconstant equal to that of the distributed-feedback control photoniccrystal of the first embodiment. Therefore, the light with the vacuumwavelength of 980 nanometers operates at the M-point in relation to thedistributed-feedback control photonic crystal. Thus, the light with thevacuum wavelength of 980 nanometers and corresponding to the M-point issubjected to two-dimensional distributed feedback by thedistributed-feedback control photonic crystal and thereby laseroscillation occurs. However, surface emission does not occur with thedistributed-feedback control photonic crystal.

A principle of the surface emission is described below. The crystalorientation of the lattice L4 of the surface-emission control photoniccrystal is the same as the crystal orientation of the lattice L3 of thedistributed-feedback control photonic crystal and the lattice constantof the lattice L4 is twice the lattice constant of the lattice L3. Thus,when reciprocal primitive vectors of the surface-emission controlphotonic crystal selected such that their magnitudes are minimum arerepresented by b₁′ and b₂′, they have the following relationship withreciprocal primitive vectors b₁ and b₂ of the distributed-feedbackphotonic crystal. Specifically, b₁′=(½)b₁ and b₂′=(½)b₁. In this state,a typical wave number vector k of a light at the M-point obtained bylaser oscillation due to distributed feedback by thedistributed-feedback control photonic crystal, k=(½)b₁+(½)b₂, can berepresented by k=b₁′+b₂′. This corresponds to the case where p=1 and q=1are assumed for a wave number vector k of the Γ-point in a reciprocallattice space of the surface-emission control photonic crystal, wherek=pb₁′+qb₂′. That is, the light obtained by laser oscillation due todistributed feedback by the distributed-feedback control photoniccrystal operates at the Γ-point in relation to the surface-emissioncontrol photonic crystal.

As a result, similar to the two-dimensional photonic crystalsurface-emitting laser according to the first embodiment, the surfaceemission is achieved by the surface-emission control photonic crystalwith the light obtained by laser oscillation due to distributed feedbackby the distributed-feedback control photonic crystal. Thetwo-dimensional photonic crystal surface-emitting laser according to thesecond embodiment is formed such that the two-dimensional distributedfeedback and the surface emission are realized using different photoniccrystal lattices. Therefore, a structure of each of the photonic crystallattices can be independently designed so that a two-dimensionaldistributed feedback effect and a surface emitting property areindependently optimized. For example, a structure of thedistributed-feedback control photonic crystal is designed to enhance adistributed feedback effect, and a structure of the surface-emissioncontrol photonic crystal is designed to increase intensity of surfaceemission by adjusting sizes of air holes.

A two-dimensional photonic crystal surface-emitting laser according to athird embodiment of the present invention is described below. Thetwo-dimensional photonic crystal surface-emitting laser according to thethird embodiment has a similar structure to those described in the firstand the second embodiments and can be manufactured by the samemanufacturing method as those described in the first and the secondembodiments. However, a surface-emission control photonic crystal formedon a GaAs photonic crystal layer is formed as a rectangular lattice witha lattice constant and a crystal orientation different from thosedescribed in the first and the second embodiments.

FIG. 6 is a plan view of a portion of a two-dimensional photonic crystalwith air holes 315 and 316 arrayed on a GaAs photonic crystal layer ofthe two-dimensional photonic crystal surface-emitting laser according tothe third embodiment. The air holes 315 form a distributed-feedbackcontrol photonic crystal with a lattice L5 as a primitive cell, and theair holes 316 form a surface-emission control photonic crystal with alattice L6 as a primitive cell. Similar to the first embodiment, alattice constant a1 of the lattice L5 is 205 nanometers and a radius ofthe air hole 315 is 49.2 nanometers, which is 0.24 times the latticeconstant a1.

The lattice L6 is arrayed such that a crystal orientation of the latticeL6 is tilted by 45 degrees from a crystal orientation of the lattice L5.A lattice constant a2 is 290 nanometers and a lattice constant a3 is 580nanometers. A radius of the air holes 316 is 30.8 nanometers, which is0.15 times the lattice constant a1. The air hole 316 is arrayed in themiddle of a predetermined two of the air holes 315.

Principles of two-dimensional distributed feedback and surface emissionof the photonic crystal according to the third embodiment are describedbelow. Similar to the distributed-feedback control photonic crystalsaccording to the first and the second embodiments, thedistributed-feedback control photonic crystal with the lattice L5 as aprimitive cell is formed as a square-lattice and has a lattice constantequal to those of the distributed-feedback control photonic crystal ofthe first and the second embodiments. Therefore, the light with thevacuum wavelength of 980 nanometers operates at the M-point in relationto the distributed-feedback control photonic crystal. Thus, the lightwith the vacuum wavelength of 980 nanometers at the M-point is subjectedto two-dimensional distributed feedback by the distributed-feedbackcontrol photonic crystal and thereby laser oscillation occurs. However,surface emission does not occur by the distributed-feedback controlphotonic crystal.

As for a principle of a surface emission, similar to the firstembodiment, a wave number vector of a light obtained by laseroscillation due to distributed feedback by the distributed-feedbackcontrol photonic crystal corresponds to a wave number vector at theΓ-point in a reciprocal lattice space of the surface-emission controlphotonic crystal. That is, the light obtained by laser oscillation dueto distributed feedback by the distributed-feedback control photoniccrystal operates at the Γ-point in relation to the surface-emissioncontrol photonic crystal.

As a result, similar to the two-dimensional photonic crystalsurface-emitting laser according to the first embodiment, the surfaceemission is achieved by the surface-emission control photonic crystalwith the light obtained by laser oscillation due to distributed feedbackby the distributed-feedback control photonic crystal. Thus, thetwo-dimensional photonic crystal surface-emitting laser according to thethird embodiment is formed such that surface emission andtwo-dimensional distributed feedback are realized using differentphotonic crystal lattices. Therefore, a structure of each of thephotonic crystal lattices can be independently designed so that atwo-dimensional distributed feedback effect and a surface emittingproperty are independently optimized. For example, a structure of thedistributed-feedback control photonic crystal is designed to enhance adistributed feedback effect, and a structure of the surface-emissioncontrol photonic crystal is designed to increase intensity of surfaceemission by adjusting sizes of air holes.

In the two-dimensional photonic crystal surface-emitting laser accordingto the third embodiment, a rectangular-lattice photonic crystal isformed such that the air holes in a square-lattice of thesurface-emission control photonic crystal of the two-dimensionalphotonic crystal surface-emitting laser according to the firstembodiment are thinned out every second line. The rectangular-lattice orother-shaped-lattice photonic crystal may be formed by thinning out theair holes using other methods so that the light obtained by laseroscillation due to distributed feedback by the distributed-feedbackcontrol photonic crystal operates at the Γ-point in relation to thesurface-emission control photonic crystal.

A two-dimensional photonic crystal surface-emitting laser according to afourth embodiment of the present invention is described below. Thetwo-dimensional photonic crystal surface-emitting laser according to thefourth embodiment has a similar structure to those described in thefirst to the third embodiments and can be manufactured by the abovemanufacturing method. However, the two-dimensional photonic crystalsurface-emitting laser according to the fourth embodiment is unique inthat it includes a photonic crystal in which two different types oftriangular-lattices with different lattice constants are superimposedone on the other.

FIG. 7 is a plan view of a portion of a two-dimensional photonic crystalwith air holes 415 and 416 arrayed on a GaAs photonic crystal layer ofthe two-dimensional photonic crystal surface-emitting laser according tothe fourth embodiment. The air holes 415 form a triangular-latticedistributed-feedback control photonic crystal with a lattice L7 as aprimitive cell, and the air holes 416 form a triangular-latticesurface-emission control photonic crystal with a lattice L8 as aprimitive cell. A lattice constant a1 of the lattice L7 is 194nanometers and a radius of the air hole 415 is 42.7 nanometers, which is0.22 times the lattice constant a1. A mode refractive index of a lightthat propagates in a InGaAs/GaAsP MQW active layer is 3.37. Therefore, amode wavelength of the light with the vacuum wavelength of 980nanometers that propagates in the InGaAs/GaAsP MQW active layer as acore is 290 nanometers. That is, the lattice constant a1 of the latticeL7 corresponds to ⅔ times the mode wavelength of the light with thevacuum wavelength of 980 nanometers.

The lattice L8 is arrayed such that a crystal orientation of the latticeL8 is tilted by 30 degrees from a crystal orientation of the lattice L7.A lattice constant a2 of the lattice L8 is 336 nanometers, which is2√3/3 times a mode wavelength of the light with the vacuum wavelength of980 nanometers. A radius of the air holes 416 is 29.1 nanometers, whichis 0.15 times the lattice constant a1. The air hole 416 is located inthe middle of predetermined two of the air holes 415. The position ofthe air hole 416 may be shifted from the middle of the predetermined twoof the air holes 415.

Principles of two-dimensional distributed feedback and surface emissionof the photonic crystal according to the fourth embodiment are describedbelow. As described above, the lattice constant a1 of the lattice L7 ofthe distributed-feedback control photonic crystal corresponds to ⅔ timesthe mode wavelength of the light with the vacuum wavelength of 980nanometers. Therefore, the mode wavelength is represented by 3a1½ andmagnitude of a wave number is 4π/(3a1). Meanwhile, a reciprocalprimitive vector of the lattice L7 is represented by b₁=(4π/(√3a1), 0)and b₂=(2π/(√3a1), 2π/a1). A wave number vector at the K-point isrepresented by k=(p+(⅓))b₁+(q+(⅓))b₂. In this state, when p=q=0 isassumed, k=(⅓)b₁+(⅓)b₂=(2π/(√3a1), 2π/(3a1)) is obtained. Thus, themagnitude of the wave number vector k is 4π/(3a1) Because the magnitudesof the wave numbers of the mode wavelength and the magnitude of the wavenumber vector at the K-point are equal, the light with the vacuumwavelength of 980 nanometers operates at the K-point in relation to thedistributed-feedback control photonic crystal.

When a light having a wave number vector corresponding to the wavenumber vector k at the K-point, where k=(⅓)b₁+(⅓)b₂, is diffracted bythe distributed-feedback control photonic crystal, the wave numbervector k changes to k′=(p′+(⅓))b₁+(q′+(⅓))b₂, where p′ and q′ arearbitrary integers. In this state, when the light is diffracted so thatp′=−1 and q′=0 are satisfied, the wave number vector k changes tok′=(−⅔)b₁+(⅓)b₂, making an angle of 120 degrees with the wave numbervector k of a light before diffraction. Therefore, a light with a wavenumber vector corresponding to the wave number vector at the K-point iscoupled with a light that travels in a direction tilted by 120 degreesfrom the light before diffraction. Furthermore, when p′=0 and q′=−1 areassumed, the wave number vector k changes to k′=(⅓)b₁−(⅔)b₂. Therefore,the light is coupled with a light that travels in a direction tilted by120 degrees from the light before diffraction. Thus, the light with thevacuum wavelength of 980 nanometers is subjected to a two-dimensionaldistributed feedback by the distributed-feedback control photoniccrystal and the laser oscillation occurs.

However, the wave number vector k′ of a diffracted light does not becomek′=0 even when any integers are substituted for p′ and q′. Therefore,surface emission does not occur by the distributed-feedback controlphotonic crystal.

A principle of the surface emission according to the fourth embodimentis described below. A crystal orientation of the lattice L8 of thesurface-emission control photonic crystal is tilted by 30 degrees from acrystal orientation of the lattice L7 of the distributed-feedbackcontrol photonic crystal and a lattice constant of the lattice L8 is √3times a lattice constant of the lattice L7. Thus, when reciprocalprimitive vectors of the surface-emission control photonic crystalselected such that their magnitudes are minimum are represented by b₁′and b₂′, they have the following relationship with reciprocal primitivevectors b₁ and b₂ of the distributed-feedback photonic crystal.Specifically, b₁′=(⅓)b₁+(⅓)b₂ and b₂′=(⅓)b₁−(⅔)b₂. In this state, atypical wave number vector k of a light obtained by laser oscillationdue to distributed feedback by the distributed-feedback control photoniccrystal, k=(⅓)b₁+(⅓)b₂, can be represented by k=b₁′. This corresponds tothe case where p=1 and q=0 are assumed for a wave number vector k at theΓ-point in a reciprocal lattice space of the surface-emission controlphotonic crystal, where k=pb₁′+qb₂′. That is, the light obtained bylaser oscillation due to distributed feedback by thedistributed-feedback control photonic crystal operates at the Γ-point inrelation to the surface-emission control photonic crystal.

As a result, similar to the two-dimensional photonic crystalsurface-emitting lasers according to the first to the third embodiments,the surface emission is achieved by the surface-emission controlphotonic crystal with the light obtained by laser oscillation due todistributed feedback by the distributed-feedback control photoniccrystal. Thus, the two-dimensional photonic crystal surface-emittinglaser according to the fourth embodiment is formed such that surfaceemission and two-dimensional distributed feedback are realized usingdifferent photonic crystal lattices. Therefore, a structure of each ofthe photonic crystal lattices can be independently designed so that atwo-dimensional distributed feedback effect and a surface emittingproperty are independently optimized. For example, a structure of thedistributed-feedback control photonic crystal is designed to enhance adistributed feedback effect, and a structure of the surface-emissioncontrol photonic crystal is designed to increase intensity of surfaceemission by adjusting sizes of air holes.

A two-dimensional photonic crystal surface-emitting laser according to afifth embodiment of the present invention is described below. Thetwo-dimensional photonic crystal surface-emitting laser according to thefifth embodiment has a similar structure to that described in the fourthembodiments and can be manufactured by the above manufacturing method.However, in the two-dimensional photonic crystal surface-emitting laseraccording to the fifth embodiment, a lattice constant and a crystalorientation of a surface-emission control photonic crystal formed on aGaAs photonic crystal layer are different from that in the fourthembodiments.

FIG. 8 is a plan view of a portion of a two-dimensional photonic crystalwith air holes 515 and 516 arrayed on a GaAs photonic crystal layer ofthe two-dimensional photonic crystal surface-emitting laser according tothe fifth embodiment. The air holes 515 form a distributed-feedbackcontrol photonic crystal with a lattice L9 as a primitive cell, and theair holes 516 form a surface-emission control photonic crystal with alattice L10 as a primitive cell. Similar to the distributed-feedbackcontrol photonic crystal of the fourth embodiment, a lattice constant a1of the lattice L9 is 194 nanometers and a radius of the air hole 515 is49.2 nanometers, which is 0.24 times the lattice constant a1.

The lattice L10 has the same crystal orientation as that of the latticeL9 and a lattice constant a2 of the lattice L10 is 388 nanometers. Aradius of the air holes 516 is 30.8 nanometers which is 0.15 times thelattice constant a1. The air hole 516 is located in the middle ofpredetermined two of the air holes 515. The position of the air hole 516may be shifted from the middle of the predetermined two of the air holes515.

Principles of two-dimensional distributed feedback and surface emissionof the photonic crystal according to the fifth embodiment are describedbelow. Similar to the distributed-feedback control photonic crystalaccording to the fourth embodiment, the distributed-feedback controlphotonic crystal with the lattice L9 as a primitive cell is formed as atriangular-lattice with the same lattice constant as the fourthembodiment. Therefore, the light with the vacuum wavelength of 980nanometers operates at the K-point in relation to thedistributed-feedback control photonic crystal. Thus, the light with thevacuum wavelength of 980 nanometers at the K-point is subjected totwo-dimensional distributed feedback by the distributed-feedback controlphotonic crystal and thereby laser oscillation occurs. However, surfaceemission does not occur by the distributed-feedback control photoniccrystal.

A principle of the surface emission according to the fifth embodiment isdescribed below. The crystal orientation of the lattice L10 of thesurface-emission control photonic crystal is the same as the crystalorientation of the lattice L9 of the distributed-feedback controlphotonic crystal and a lattice constant of the lattice L10 is twice thelattice constant of the lattice L9. Thus, when reciprocal primitivevectors of the surface-emission control photonic crystal selected suchthat their magnitudes are minimum are represented by b₁′ and b₂′, theyhave the following relationship with reciprocal primitive vectors b₁ andb₂ of the distributed-feedback photonic crystal. Specifically, b₁′=(⅓)b₁and b₂′=(⅓)b₂. In this state, a typical wave number vector k of a lightobtained by laser oscillation due to distributed feedback by thedistributed-feedback control photonic crystal, k=(⅓)b₁+(⅓)b₂, can berepresented by k=b₁′+b₂′. This corresponds the case where p=1 and q=1are assumed for a wave number vector k of the Γ-point in a reciprocallattice space of the surface-emission control photonic crystal, wherek=pb₁′+qb₂′. That is, the light obtained by laser oscillation due todistributed feedback by the distributed-feedback control photoniccrystal operates at the Γ-point in relation to the surface-emissioncontrol photonic crystal.

As a result, similar to the two-dimensional photonic crystalsurface-emitting laser according to the fourth embodiment, the surfaceemission is achieved by the surface-emission control photonic crystalwith the light obtained by laser oscillation due to distributed feedbackby the distributed-feedback control photonic crystal. Thus, thetwo-dimensional photonic crystal surface-emitting laser according to thefifth embodiment is formed such that the two-dimensional distributedfeedback and the surface emission are realized using different photoniccrystal lattices. Therefore, a structure of each of the photonic crystallattices can be independently designed so that a two-dimensionaldistributed feedback effect and a surface emitting property areindependently optimized. For example, a structure of thedistributed-feedback control photonic crystal is designed to enhance adistributed feedback effect, and a structure of the surface-emissioncontrol photonic crystal is designed to increase intensity of surfaceemission by adjusting sizes of air holes.

A two-dimensional photonic crystal surface-emitting laser according to asixth embodiment of the present invention is described below. Thetwo-dimensional photonic crystal surface-emitting laser according to thesixth embodiment has a similar structure to that described in the firstembodiment shown in FIG. 1 and can be manufactured by the samemanufacturing method. However, in the two-dimensional photonic crystalsurface-emitting laser according to the sixth embodiment, air holes thatform a surface-emission photonic crystal formed on a GaAs photoniccrystal layer have different sizes depending on positions in a planedirection of the GaAs photonic crystal layer.

FIG. 9 is an exploded perspective view of a two-dimensional photoniccrystal surface-emitting laser 600 according to the sixth embodiment,wherein an in-plane center portion and a peripheral portion of the GaAsphotonic crystal layer 606 are enlarged. The two-dimensional photoniccrystal surface-emitting laser 600 has a similar structure to that ofthe two-dimensional photonic crystal surface-emitting laser 100according to the first embodiment. Air holes 615 that form adistributed-feedback control photonic crystal are formed as asquare-lattice with a lattice constant equal to that of the air holes115 in the two-dimensional photonic crystal surface-emitting laser 100according to the first embodiment. A radius of the air hole 615 is 49.2nanometers, which is 0.24 times the lattice constant a1, and uniformregardless of in-plane positions in the GaAs photonic crystal layer 606.

Air holes 616 that form a surface-emission control photonic crystal areformed as a square-lattice with a lattice constant equal to that of theair holes 116 in the two-dimensional photonic crystal surface-emittinglaser 100 according to the first embodiment, and with the same crystalorientation as the first embodiment. However, radiuses of the air holes616 are different depending on the in-plane positions in the GaAsphotonic crystal layer 606. In FIG. 9, in a dotted-line circle indicatedby a reference symbol A, the air holes 615 and air holes 616 a on acenter portion in the in-plane direction of the GaAs photonic crystallayer 606 are shown; and in a dotted-line circle indicated by areference symbol B, the air holes 615 and air holes 616 b on aperipheral portion are shown. A radius of the air hole 616 b that formthe peripheral portion of the surface-emission control photonic crystalis smaller than a radius of the air hole 616 a that form the centerportion of the surface-emission control photonic crystal. Specifically,a radius of the air hole in the center portion is 32.8 nanometers whichis 0.16 times the lattice constant a1 of the lattice L1, that is, 205nanometers, and a radius exponentially decreases with an in-planedistance from the center portion to the peripheral portion. A radius ofan air hole on a position 50 micrometers away from the center portion is16.4 nanometers, which is a half of that on the center portion.

By setting the radius of the air holes of the surface-emission controlphotonic crystal such that the radius of the air holes on the in-planecenter portion of the photonic crystal layer are larger than the radiusof the air holes on the peripheral portion, the surface emission effectof the surface-emission control photonic crystal by grating couple ismade larger in the center portion and smaller in the peripheral portion.As a result, it is possible to output a laser beam having aGaussian-like field distribution in the in-plane direction. According tothe sixth embodiment, the radius of the air holes are exponentiallychanged depending on a distance from the center portion, so that a lightwith a Gaussian-like field distribution in the in-plane direction isobtained. However, the size of the air holes may be changed by usingother methods depending on a desired shape of a beam.

A two-dimensional photonic crystal surface-emitting laser according to aseventh embodiment of the present invention is described below. In thetwo-dimensional photonic crystal surface-emitting laser according to theseventh embodiment, similarly to the sixth embodiment, air holes of asurface-emission photonic crystal formed on a GaAs photonic crystallayer have different sizes depending on in-plane positions in the GaAsphotonic crystal layer, and the photonic crystal lattice is formed as atriangular-lattice.

FIG. 10 is an exploded perspective view of a two-dimensional photoniccrystal surface-emitting laser 700 according to the seventh embodiment,wherein an in-plane center portion and a peripheral portion of a GaAsphotonic crystal layer 706 are enlarged in dotted-line circles indicatedby reference symbols C and D. In the two-dimensional photonic crystalsurface-emitting laser 700, air holes 715 that form adistributed-feedback control photonic crystal are formed as atriangular-lattice with a lattice constant equal to that of the airholes 415 in the two-dimensional photonic crystal surface-emitting laseraccording to the fourth embodiment. A radius of the air hole 715 is 42.7nanometers which is 0.22 times the lattice constant of the lattice L7,that is, 194 nanometers, and uniform regardless of in-plane positions inthe GaAs photonic crystal layer 706.

Air holes 716 of a surface-emission control photonic crystal are formedas a triangular-lattice with a lattice constant equal to that of the airholes 416 in the two-dimensional photonic crystal surface-emitting laseraccording to the fourth embodiment, and with the same crystalorientation as the fourth embodiment. However, radiuses of the air holes716 are different depending on the in-plane positions in the GaAsphotonic crystal layer 706. In FIG. 10, an enlarged view of the airholes 715 and air holes 716 a on a center portion in the in-planedirection of a GaAs photonic crystal layer 706 a is shown in adotted-line circle indicated by a reference symbol C; and an enlargedview of the air holes 715 and air holes 716 b on a peripheral portion isshown in a dotted-line circle indicated by a reference symbol D. Aradius of the air hole 716 b in the peripheral portion of thesurface-emission control photonic crystal is smaller than a radius ofthe air hole 716 a in the center portion of the surface-emission controlphotonic crystal. Specifically, a radius of the air hole in the centerportion is 31 nanometers which is 0.16 times the lattice constant of thelattice L7, that is, 194 nanometers, and a radius exponentiallydecreases with an in-plane distance from the center portion to theperipheral portion. A radius of an air hole on a position 50 micrometersaway from the center portion is 15.5 nanometers, which is a half of thatof the center portion.

According to the seventh embodiment, similar to the sixth embodiment, bysetting the radius of the air holes of the surface-emission controlphotonic crystal such that the radius of the air holes on the in-planecenter portion of the photonic crystal layer are larger than the radiusof the air holes on the peripheral portion, the surface emission effectof the surface-emission control photonic crystal by grating couple ismade larger in the center portion and smaller in the peripheral portion.As a result, it is possible to output a laser beam having aGaussian-like field distribution in the in-plane direction. Furthermore,the size of the air holes may be changed by using other methodsdepending on a desired shape of a beam.

As described above, according to an aspect of the present invention, thedistributed-feedback control photonic crystal and the surface-emissioncontrol photonic crystal are superimposed one on the other in thetwo-dimensional photonic crystal surface-emitting laser. Specifically,the distributed-feedback control photonic crystal is configured so thata light that propagates in an active layer as a core is subjected totwo-dimensional distributed feedback and the surface-emission controlphotonic crystal is configured so that the surface emission occurs withthe propagated light. Therefore, it is possible to provide thetwo-dimensional photonic crystal surface-emitting laser in which thetwo-dimensional feedback effect and the surface emitting property areindependently controlled.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. A two-dimensional photonic crystal surface-emitting laser comprising:an active layer that emits a light with a carrier injection; a mediumlayer formed near the active layer; and a two-dimensional photoniccrystal formed in the medium layer by arranging a medium having arefractive index different from that of the medium layer in a latticepattern, wherein the two-dimensional photonic crystal includes adistributed-feedback control photonic crystal in which a lightpropagating through the active layer as a core is subjected to atwo-dimensional distributed feedback within a plane of the active layer,and the light is not radiated in a direction normal to the plane of theactive layer, and a surface-emission control photonic crystal in whichthe light is radiated in the direction normal to the plane of the activelayer, and the distributed-feedback control photonic crystal and thesurface-emission control photonic crystal are superimposed with eachother.
 2. The two-dimensional photonic crystal surface-emitting laseraccording to claim 1, wherein the distributed-feedback control photoniccrystal is formed as a square-lattice with a lattice constant which is1/√2 times a mode wavelength of the light, and the surface-emissioncontrol photonic crystal is formed as a square-lattice with a latticeconstant equal to the mode wavelength of the light and with a crystalorientation making an angle of 45 degrees with a crystal orientation ofthe distributed-feedback control photonic crystal.
 3. Thetwo-dimensional photonic crystal surface-emitting laser according toclaim 1, wherein the distributed-feedback control photonic crystal isformed as a square-lattice such that the light operates at an M-point ina wave number space at a mode wavelength of the light, where the M-pointis a symmetrical point represented by (p+(½))b₁+(q+(½))b₂, where p and qare arbitrary integers, and b₁ and b₂ are reciprocal primitive vectorswith minimum magnitudes of the photonic crystal lattice in the wavenumber space, and the surface-emission control photonic crystal isformed as a rectangular lattice such that the light operates at aΓ-point in a wave number space at the mode wavelength of the light,where the Γ-point is a symmetrical point represented by pb₁+qb₂.
 4. Thetwo-dimensional photonic crystal surface-emitting laser according toclaim 1, wherein the distributed-feedback control photonic crystal isformed as a triangular-lattice with a lattice constant which is ⅔ timesa mode wavelength of the light, and the surface-emission controlphotonic crystal is formed as a triangular-lattice with a latticeconstant which is 2√3/3 times the mode wavelength of the light and witha crystal orientation making an angle of 30 degrees with a crystalorientation of the distributed-feedback control photonic crystal.
 5. Thetwo-dimensional photonic crystal surface-emitting laser according toclaim 1, wherein the distributed-feedback control photonic crystal isformed as a triangular-lattice such that the light operates at a K-pointin a wave number space at a mode wavelength of the light, where theK-point is a symmetrical point represented by (p+(⅓))b₁+(q+(⅓))b₂ or(p−(⅓))b₁+(q+(⅔))b₂, where p and q are arbitrary integers, and b₁ and b₂are reciprocal primitive vectors with minimum magnitudes of the photoniccrystal lattice in the wave number space, and the surface-emissioncontrol photonic crystal is formed as a triangular-lattice such that thelight operates at a Γ-point in a wave number space at the modewavelength of the light, where the Γ-point is a symmetrical pointrepresented by pb₁+qb₂.
 6. The two-dimensional photonic crystalsurface-emitting laser according to claim 1, wherein sizes of the mediumare different depending on an in-plane position in the medium layer. 7.The two-dimensional photonic crystal surface-emitting laser according toclaim 2, wherein sizes of the medium are different depending on anin-plane position in the medium layer.
 8. The two-dimensional photoniccrystal surface-emitting laser according to claim 3, wherein sizes ofthe medium are different depending on an in-plane position in the mediumlayer.
 9. The two-dimensional photonic crystal surface-emitting laseraccording to claim 4, wherein sizes of the medium are differentdepending on an in-plane position in the medium layer.
 10. Thetwo-dimensional photonic crystal surface-emitting laser according toclaim 5, wherein sizes of the medium are different depending on anin-plane position in the medium layer.
 11. The two-dimensional photoniccrystal surface-emitting laser according to claim 6, wherein sizes ofthe medium decrease exponentially from a center portion to a peripheralportion in the plane direction of the medium layer.
 12. Thetwo-dimensional photonic crystal surface-emitting laser according toclaim 7, wherein sizes of the medium decrease exponentially from acenter portion to a peripheral portion in the plane direction of themedium layer.
 13. The two-dimensional photonic crystal surface-emittinglaser according to claim 8, wherein sizes of the medium decreaseexponentially from a center portion to a peripheral portion in the planedirection of the medium layer.
 14. The two-dimensional photonic crystalsurface-emitting laser according to claim 9, wherein sizes of the mediumdecrease exponentially from a center portion to a peripheral portion inthe plane direction of the medium layer.
 15. The two-dimensionalphotonic crystal surface-emitting laser according to claim 10, whereinsizes of the medium decrease exponentially from a center portion to aperipheral portion in the plane direction of the medium layer.